Child porn is the emotional argument, the only possible case where most people might agree that some content can be illegal. A more representative scenario is illegal copies of music or a political pamphlet in China.

Sorry, how is child porn only an appeal to emotion?

Never said it was "only" an appeal to emotion, just that it's not representative. It's meant to stop discussion before it starts.

A question that you can’t answer isn’t the same as one meant to shut down discussion

Open questions :

1) If childporn was not banned, how many people would consume that content anyway?

2) What about hyper-photorealistic childporn movies with fictional characters and future rendering technologies? How will you tell the video is true or not and worth to be removed?

Technological progress will not stop because some people abuse the technology.